1. Field of the Invention
This invention relates to arc extinguishing devices for electrical switchgear such as air break disconnect switches used in transmission and distribution lines.
2. Related Art
U.S. Pat. No. 6,392,181, May 21, 2002, also assigned to Cleaveland/Price Inc., describes relevant background concerning use of high speed whips of all metal construction in arc extinguishing devices of switches and further describes such apparatus with whips comprising a nonmetallic material , such as a plastic polymer member, with a flexible conductive path. The patent describes embodiments capable of achieving faster separation (with less chance of arc restriking) of a whip with nonmetallic material as compared to an all metal whip that is otherwise similar.
All such description of the patent related to all metal whips of the background art and, also, whips with nonmetallic material newly presented in the patent, is incorporated herein by reference.
The present invention is directed to apparatus generally like that of the above-mentioned patent, with a whip comprising a nonmetallic material, such as a plastic polymer, with a flexible conductive path, with newly disclosed embodiments of the whip itself and, in addition, of the latch or hook element that the whip makes conductive contact with during initial main contact separation.
Some of the various example embodiments of the invention include one or more of the following innovative features.
A whip in one form comprises a plurality of tapered nonmetallic rods that fit inside one another. For example, a first hollow rod has one or more additional tapered rods telescopically fit together inside the first rod forming a rod assembly. At least all but the final, inner rod is hollow. Only the outer-most rod needs to be provided with a conductive path. The plurality of rods can be of the same nonmetallic material and have the same taper dimensions. Fitting the rods together only requires a second rod to be inserted in the first rod to the extent the first and second rods dimensions allow, generally with the tip of the second rod at least halfway through the length of the first, and the tip of a third, if any, at least halfway through the second. Most often the extent of the inserted rod is about 75% to 90% through the length of the adjacent outer rod. The assembled rods are terminated at a common blunt end. In some embodiments three or four rods have been so assembled and have exhibited good characteristics but the number of rods may be varied.
An assembly of multiple rods as described is considered to perform similar to a leaf spring with an increase in accelerating force, compared to use of a single rod like the first rod of the assembly, while still retaining flexibility. The multiple rods also can be more resistant to breakage than a single unitary rod of the same overall dimensions as the multiple rods.
Such an assembly of multiple rods is provided with a conductive path for engaging with a latch of an arc extinguishing device such as described in the above patent and in other descriptions below. For example, the outer surface of the first rod has some from of a conductor layer on it.
The conductive path on the outer rod of the rod assembly (or a single rod where only one is used) can be formed in numerous different ways to achieve desired conduction between the whip and the latch and between the latch contact point and the attachment of the whip to the switch contact arm, all while the nonmetallic rod supporting the conductive path still retains substantial flexibility so it can provide higher separation speed from the latch.
The forms described herein for the conductive path on the nonmetallic rod include, for example, at least one conductor selected from the group consisting of a metal braid (e.g., tubular metal braid held to the rod by its own elasticity), a metal foil (e.g., a wrapping of an adhesive backed thin foil layer), a metal sheath (e.g., a conductive tubular element into which the nonmetal rod fits securely), and a wound metal wire. Various examples, including combinations of some of the foregoing conductors, will be described, of which some are particularly designed to enhance the durability of the conductive path where arcing is initiated between the whip and the latch upon switch closing and also at the tip of the whip that finally separates from the latch.
Among embodiments of the invention are those in which a nonmetallic portion of a whip, such as a rod assembly with the multiple rods above described or a single nonmetallic rod, is assembled with an all metal base portion with the metal portion extending, for example, from a point of connection on a switch contact arm to a point above an area on the whip at which it first conducts when the switch contacts open and also where it first has a close air gap with the latch during switch closing. In such embodiments, the metal base portion can be like the base part of the prior art all metal whips. A whip with an all metal base can allow repeated switch operations with as much durability as prior whips entirely of metal. The whip portion with a nonmetallic rod plus a conductive path at the tip end of the whip can give favorable separation speed of the whip from the latch to minimize arcing on switch opening. The metal base portion can also contribute to increasing the separation speed by storing spring force during flexing of the whip.
A further feature of the invention involves a modification of the latch of the device so it has a wheel that engages the whip during part of a switch opening. The rolling wheel surface is the final release point for the whip from the latch. It can reduce the sliding wear between the latch and the conductor on the whip surface.
These and other aspects of the present invention will be further understood from the entirety of the description, drawings and claims.